This invention relates to electrochromic display devices.
Traditionally, electrochromic display devices have been in a xe2x80x9csandwichxe2x80x9d configuration. Sandwich devices use vertically arranged electrodes with at least one transparent electrode at the viewable surface of the device. In light of difficulties such as low conductivity, difficulty of manufacture, and potential corrosion especially in aqueous systems, devices have been developed which are not configured in a sandwich arrangement. Such devices do not require transparent electrodes at the viewable surface. Instead of a transparent electrode at the viewable surfaces, these devices have a gelled electrolyte at the viewable surface. The electrodes are not vertically arranged. Rather, they are present in a same plane.
In electrochromic devices using the side-by-side or interidigitated in plane configured electrodes, an ionically conductive transparent gelled electrolytic layer is placed on top of the electrochromic layer under a transparent polyester or polyimide film. To activate the electrochromic layer, interdigitated or side-by-side counter and working electrodes are printed on a bottom substrate. Because a high conductivity gelled electrolyte is used, the resistivity of the electrolyte is much less than the resistivity of the electrochromic layer. This concept has been extended to the use of a gelled visible layer containing an electrolyte to include a double-sided electrochromic display. Like side-by-side systems, the double-sided device does not require a transparent electrically conductive electrode at the viewable surface.
Nonetheless, gelled aqueous electrolytes present a water barrier problem for devices fabricated on plastic films, such as PET. Typically, PET and other plastic films are poor water vapor barriers. Water loss can significantly impact the lifetime and reliability of the device.
Applicants have invented new electrochromic devices where interdigitated drive architecture can be used while the undesirable aspects of using aqueous electrolytes or gelled aqueous electrolytes can be avoided.
According to a first embodiment the invention is a display device comprising a solid transparent, charge conducting material, positioned below the transparent solid material, an active layer comprising an electrochromic material and an electrolyte; and positioned below the active layer a working electrode and a counter-electrode arranged such that they are isolated from one another, wherein the distance between the working and the counter electrode is greater than two times the thickness of the active layer between the electrode and the transparent conductive material.
According to a second embodiment the invention is a display device comprising a transparent, charge conducting material and below the transparent material is an active layer comprising compound (a) a non-aqueous compound that undergoes an electron transfer reaction with a subsequent change in its protic state resulting in a pH gradient in the device, (b) at least one indicator dye, and (c) a charge transport material, and positioned below the active layer a working electrode and a counter electrode arranged such that they are isolated from one another, wherein the distance between the working layer and the counter electrode is greater than two times the thickness of the active layer between the electrode and the transparent conductive material.
According to a third embodiment the invention is a display device comprising a transparent conducting material, and below the transparent material is an active layer comprising (a) a compound that undergoes an electron transfer reaction with subsequent change in its protic state, (b) at least one indicator dye which changes color when a change in pH occurs, and (c) an ionically conductive material and optionally component (d), a matrix material, wherein components (a), (b), (c) and (d) are different from one another and component (a) preferentially undergoes the electron transfer reaction when a charge is applied to the composition and positioned below the active layer a working electrode and a counter electrode such that they are arranged isolated from one another, where in the distance between the working layer and the counter electrode is greater than two times the thickness of the active layer between the electrode and the transparent conductive material.